Shipping and storage container for high power density radioactive materials

ABSTRACT

A shipping and storage container for radioactive material, particularly high thermal producing fissile material, which includes a cylindrical inner metal container for retaining the radioactive material, an alpha contamination barrier of polyvinyl chloride surrounding said inner container, a cylindrical outer metal container enclosing said inner container and barrier with inner surfaces spaced from the inner container walls and from said barrier, and finely divided heat absorbing and transferring or conducting magnesium oxide filling the space intermediate said barrier and the inner surfaces of the outer metal container.

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OR 3a75 19l 1-l United States Pf Leebl et al.

[ SHIPPING AND STORAGE CONTAINER FOR HIGH POWER DENSITY RADIOACTIVEMATERIALS [75] Inventors: Robert G. Leebl, Arvada, Colo.;

Robert L. Sandvig, Rapid City, S. Dak.; Edward Vejvoda, Boulder, C010.

[73] Assignee: The United States of America as represented by the UnitedStates Atomic Energy Commission, Washington, D.C.

[22] Filed: July 12, 1972 [21] Appl. No.: 270,885

[52] US. Cl 250/507 [51] Int. Cl. G2lf 3/00 [58] Field of Search 250/108R, 108 WS,

[56] References Cited UNITED STATES PATENTS Bruno et al. 250/108 R Nashet al. 250/108 R Princiotta et al. 250/108 R Primary Examiner-James W.Lawrence Assistant Examiner-Davis L. Willis AttorneyRoland A. Anderson[5 7 ABSTRACT A shipping and storage container for radioactive material,particularly high thermal producing fissile material, which includes acylindrical inner metal container for retaining the radioactivematerial, an alpha contamination barrier of polyvinyl chloridesurrounding said inner container, a cylindrical outer metal container enclosing said inner container and barrier with inner surfaces spaced fromthe inner container walls and from said barrier, and finely divided heatabsorbing and transferring or conducting magnesium oxide filling thespace intermediate said barrier and the inner surfaces of the outermetal container.

3 Claims, 2 Drawing Figures Patented Aug. 21, 1973 3,754,141

SHIPPING AND STORAGE CONTAINER FOR HIGH POWER DENSITY RADIOACTIVEMATERIALS BACKGROUND OF INVENTION Radioactive materials may be stored inappropriate containers for various reasons between uses thereof orbetween production and use and must often be shipped or transported fromone location to another while so stored. These materials, because oftheir radioactivity and any other inherent toxicity must be stored in acontainer which will reliably contain the same regardless of theenvironmental conditions under which the storage and/or shippingcontainer may be subjected. In turn, it is also desirable, thatwhichever materials that the storage or shipping containers are formedof are not such that will produce or give off material or gases whichmay contaminate the radioactive material and which might prevent its usefor an intended purpose.

The storage and shipping of radioactive material becomes increasinglymore difficult when the material exhibits a high degree of radioactivitytogether with a high production of thermal energy. Materials which maywithstand a certain amount of radioactivity at low temperatures mayrapidly degrade under the combined effects of heat and radiation. Thus,the storage of such materials as fissile plutonium dioxide with highspecific power outputs may prevent storage or shipping of this materialin ordinarily acceptable container configuration and materials orrequire its shipping or storage in uneconomically small quantities. Forexample, polyvinyl chloride bags or sheets used either alone or incombination with other containers to hold radioactive materials, whensubjected to temperatures above about 200F in alpha and gamma radiation,rapidly degrade with appreciable decrease in strength and contaminantcapabilities. In addition, during such degradation of polyvinylchloride, both hydrogen gas and hydrochloric vapors are evolved whichmay react with the radioactive material to contaminate the same as wellas attack the container. Further, the so degraded polyvinyl chloridebecomes more permeable to air and moisture which in turn may causeadditional decomposition or contamination of the radioactive material,particularly under the high temperature conditions resulting from thehigh thermal energy production of high specific power radioactivematerials. In addition, the degradation and failure of the polyvinylchloride bag used to remove a radioactive material container from aglovebox line would permit the spread of radioactive contamination fromthe outside surface of the container and the inside surface of thepolyvinyl chloride bag as well as other parts of the storage system.

It would be desirable to provide a storage and shipping container whichis of simple and relatively low cost construction and which will providethe desired long term protection of high specific power radioactivematerials without release or contamination of such.

SUMMARY OF INVENTION In view of the above, it is an object of thisinvention to provide a storage and shipping container which is of simpleand low cost construction.

It is a further object of this invention to provide a storage andshipping container which utilizes a polyvinyl chloride alpha radiationcontamination barrier.

It is a further object of this invention to provide a high specificpower plutonium oxide storing and shipping container utilizingrelatively low cost and reusable materials.

Various other objects and advantages will appear from the followingdescription of the invention and the most novel features will be pointedout hereinafter in connection with the appended claims. It will beunderstood that various changes in the details, materials andarrangements of the parts, which are herein described and illustrated inorder to explain the nature of the invention, may be made by thoseskilled in the art.

The invention comprises a radioactive-materialenclosing inner metalcontainer, a polyvinyl chloride alpha radiation barrier enclosing saidinner container, a metal outer container surrounding and spaced fromsaid inner container and said barrier, and heat absorbing andtransferring or conducting magnesium oxide powder filling the spaceintermediate said outer container and said polyvinyl barrier to maintainthe barrier in close contact with said inner container and for absorbingand transferring or conducting heat away from the latter.

DESCRIPTION OF DRAWING The invention is illustrated in the accompanyingdrawing wherein:

FIG. I is a cross-sectional view of the storage and shipping containerof this invention; and

FIG. 2 is an elevation side view partially in cross section of ashipping system utilizing the container of FIG. 1.

DETAILED DESCRIPTION The storage and shipping container 10 shown in FIG.1 may be used or employed to hold radioactive material for appreciabletime periods without significant degradation of the container materialsand without release or contamination of the radioactive material itselfor the component parts of the shipping system. This successfulcontainment of radioactive material is achieved for long periods of timeeven using radioactive material having high thermal energy productionand high specific power with significant amounts of even highlycorrosive forms of plutonium.

The storage and shipping container arrangement 10 includes a cylindricalor tubular inner or primary container 12 having a central bore or cavityopen at one end and closed at the other for receiving the radioactivematerial 14 therein. The open end of container 12 is closed by anappropriate removable cover 16 which may be suitably attached tocontainer 12 by the threaded portions shown, or the like, to form acomplete, enclosed chamber for retention of material 14. An appropriategasket or an unperforate liner I8 may be provided between the end cap orcover 16 and container 12, either as shown or within the threadedportions or other mating portions thereof, to prevent release ofmaterial I4 from container 12 and to hermetically seal or contain anygas pressure buildup which may occur within container 12 fromradioactive decay of material 14 or from increased heat buildup thereinand resulting expansion of enclosed gases or solids. Gasket or liner 18may be formed from polytetrafluoroethylene thread gasket material, whichwill also act to inhibit galling or other damage to the threads thatcould lead to a failure of the seal between end cap 16 and container 12should such damage occur and permit reuse of the container and cover.The container 12 with end cap 16 should preferably be made of acorrosion resistant and heat conductive material which is also notsubject to objectionable heat degradation and which is compatible withthe radioactive material 14 being contained under all environmentalconditions to which the container and radioactive material may besubjected. Fro plutonium oxide containment, the container and end capare preferably made from 300 series stainless steel. For convenience,container 12 may be made from commercially available stainless steelpipe threaded at one end and sealed at the other end with a welded platewhile end cap 16 may be a conventional threaded stainless steel pipecap.

A polyvinyl chloride bag or container 20, shown with exaggeratedthickness for illustration purposes, of appropriate shape is disposedabout and in close or in an initial relatively close contact with theouter surfaces of inner container 12 and end cap 16 and the open end orends or openings of bag 20 closed and sealed by application of heat or asealant or by an appropriate clamping member 22 or tightly encirclingsealing tape. The bag 20 should be made of a polyvinyl chloride film orsheet having a sufficient thickness to provide an alpha contaminationbarrier and is preferably of thickness of from about 0.01 inch to 0.015inch, for convenience of handling. Bag 20 may be a tube of polyvinylchloride sheet sealed and clamped or closed at both ends or it may be inthe form of a container as shown in FIG. 1 having a single open end forreceiving container 12 which is then sealed by clamp 22. Clamp 22 may beany appropriate device or material which will gather and hold thepolyvinyl chloride film and seal the same about said opening and may beof such as pigmented vinyl plastic adhesive tape or the like, or thebarrier may be heat sealed to itself. The polyvinyl chloride bag is aconvenient mechanism to remove the primary container from a glovebox orother handling container and to serve as the initial alpha radioactivitycontainment barrier.

The polyvinyl chloride alpha barrier enclosed inner cylindrical ortubular container 12 is then positioned within a cylindrical or tubularouter container 24 with all inner surfaces thereof spaced from all outersurfaces of inner container 12 and end cap 16 and from the outersurfaces of barrier 20. The remaining internal cavity or space incontainer 24 is completely filled and gravity or otherwise tamped withfinely divided heat absorbing and transmitting or conducting magnesiumoxide 26 about the outer surfaces of and in intimate contact withbarrier 20 so as to maintain barrier 20 in close contact with container12 and end cap 16 for ready absorption and transfer or conduction ofheat away from container 12, end cap 16 and barrier 20. Container 24 isenclosed and sealed by an appropriate cover or lid 28 using suitablecrimping or other closure techniques and, if desired, suitably sealed byappropriate sealants, gaskets or the like. The finely divided magnesiumoxide 26 is preferably in a powder or particle form of less than about200 microns (new US. Standard sieve size) in size and of high purity toinsure high levels of heat absorption and transferability orconductivity. Commercially available magnesium oxide sand of 80 meshwith less than 2 percent silicon has been found to be particularlyappropriate. Greater particle sizes may be used, however, withdecreasing thermal absorption and transfer or conductivity capabilities.Magnesium oxide powder of about 180 micron size gravity tamped toachieve a good level of contact between particle surfaces exhibits athermal conductivity of about 0.392 Btu/ft-hr-F. Such magnesium oxidepowder is also non-burning, relatively stable, provides shockabsorption, and exhibits a high melting point, all of whichcharacteristics are desirable in the storage and shipping container 10.Container 24 may be made of any appropriate metal, such as steel, whichwill provide good thermal conductivity as well as sufficient strength toretain the materials enclosed therein under the environmental conditionsto which they are to be subjected, and for convenience, may be acommercially available steel can. it is generally desirable thatcontainer 12 be spaced from all inner surfaces of container 24 by atleast about 1 inch to provide sufficient shock absorbing capabilitiesand a desired temperature gradient between the radioactive material 14and the exterior of container 10.

A storage and shipping container 10 was made by utilizing a 1.5 inch asnominal diameter series 300 stainless steel pipe threaded at one end andsealed at the other end with a welded plate, the pipe and plate havingwall thicknesses of about 0.145 inch and an overall length of about 6.5inches as inner container 12. A standard threaded stainless steel pipecap with a polytetrafluoroethylene gasket was threaded over the open endof container 12 after filling the interior thereof with about 800 gramsof plutonium oxide, which may include americium-24l oxide or otherradioactive materials. The loaded container 12 was then enclosed withina polyvinyl chloride tube of about 0.01 inch film thickness and the endsthereof gathered and sealed by adhesive-backed, pigmented vinyl plastictape, thus facilitating removal of container 12 from a glovebox andprotection of personnel from alpha radioactivity. The bagged containerwas then placed into a standard No. mild steel can having approximately4 inches outside diameter by 9 inches in height after disposing andgravity tamping about 1 inch of magnesium oxide powder at the bottomthereof. The can, that is outside container 24, was then filled in thespaces between its inner surfaces and the outer surfaces of the barrier20 with additional finely divided magnesium oxide and the same gravitytamped. A cover was then crimped and sealed over the can to complete thestorage and shipping container 10.

Storage and shipping containers as so described were filled withradioactive plutonium oxide materials having specific powers from about2 to about 7 watts per kilogram with corresponding total power thermaloutput of from about 1.5 to about 5.5 watts. The maximum temperature ofthe container 10 enclosing the highest specific power radioactivematerial was about 1 10F. It was found that the polyvinyl chloridebarrier 20 did not change in texture, appearance or apparent strengtheven when subjected to a temperature at the outside of container 12 ofabout 148F for about hours and a temperature of about 122F for about 200hours. The storage and shipping container 10 constructed as describedmay contain radioactive material producing up to 9 or [0 thermal wattswithout producing a temperature greater than 200F at the exteriorsurface of container 12, and at such temperature the polyvinyl chloride,even in the radiation environment, is not noticeably degraded over longperiods of exposure time.

Storage and shipping container 10 may be positioned within a standard,commercially available shipping container system, as shown in FIG. 2, toprovide complete and acceptable radiation and other protection under allsituations. This shipping container system may include an innercontainer 30 and cover 32 for receiving and holding container 10, anouter container 34 and cover 36, and an intermediate shock absorbingmedium 38 and 40 disposed about container 30 on all sides thereof. Sucha shipping system may meet all requirements of safe conductance ofradioactive materials in normal channels of transportation.

What is claimed is:

l. A plutonium oxides shipping package comprising a cylindricalgas-tight inner container of heat conductive and corrosion resistantmetal for retaining plutonium oxides having heat output of up to aboutthermal watts, a flexible alpha contamination barrier of polyvinylchloride of from about 0.01 inch to 0.015 inch thickness completelyenclosing and in intimate heat conducting contact with cylindrical outersurfaces with all inner surfaces spaced from all outer surfaces of theinner metal container and with inner cylindrical surfaces spaced atleast one inch from outer cylindrical surfaces of the inner metalcontainer, and solely finely divided heat conducting magnesium oxide ofabout 80 mesh filling the space intennediate said polyvinyl chloridebarrier and inner surface of the outer metal container and maintainingsaid barrier in said intimate heat conducting contact with said outersurfaces of the inner metal ontainer for conducting heat away from thelatter.

2. A shipping package as claimed in claim 1 wherein said inner containercomprises complementary screwthreaded interfitting side wall portionswith a joint therebetween and a polytetrafluoroethylene gasket sealingthe joint between said portions.

3. A shipping package as claimed in claim 1 wherein said inner containerhas an inner diameter of about 1.5

of said inner container, a cylindrical outer container of inches and awall thickness of about 0.15 inches.

heat conducting metal enclosing said inner container

2. A shipping package as claimed in claim 1 wherein said inner containercomprises complementary screw-threaded interfitting side wall portionswith a joint therebetween and a polytetrafluoroethylene gasket sealingthe joint between said portions.
 3. A shipping package as claimed inclaim 1 wherein said inner container has an inner diameter of about 1.5inches and a wall thickness of about 0.15 inches.